TUESDAY, March 18, 2014 (HealthDay News) -- Expectant mothers should not get fetal ultrasound videos as keepsakes and should not use over-the-counter Doppler ultrasound heartbeat monitors, according to the U.S. Food and Drug Administration.

Although both products are generally considered safe, they are approved for use only with a prescription. The increasing use of these devices for nonmedical reasons is raising concerns among health officials.

"Although there are no known risks of ultrasound imaging and heartbeat monitors, the radiation associated with them can produce effects on the body," Robert Phillips, a physicist with the FDA's Center for Devices and Radiological Health, said in an agency news release.

"When ultrasound enters the body, it heats the tissues slightly," Phillips said. "In some cases, it can also produce small pockets of gas in body fluids or tissues."

The long-term impact of these effects is not known, Phillips said.

"Performing prenatal ultrasounds without medical oversight may put a mother and her unborn baby at risk," he said. "The bottom line is: Why take a chance with your baby's health for the sake of a video?"

In some cases, when mothers get keepsake videos of their fetus, an ultrasound machine may be used for as long as an hour, Phillips said.

The FDA is also concerned about over-the-counter sales of Doppler ultrasound heartbeat monitors, which are used to listen to a fetus's heartbeat. The agency says these devices should be used only by or under the supervision of a health care professional.

"When the product is purchased over the counter and used without prior consultation with a health care professional, there is no oversight of how the device is used and little or no medical benefit derived from the exposure," Phillips said. "The number of sessions or the length of a session to which a fetus is exposed is uncontrolled, thus raising the potential for harm to the fetus."